1. Field of the Invention
The present invention relates to a radiation shielding members including nano-particles as a radiation shielding material and to a method for preparing the same.
2. Description of the Related Art
Radiation is largely classified into ionizing radiation and non-ionizing radiation, while radiation typically designates ionizing radiation in general.
Ionizing radiation includes alpha rays, beta rays, protons, neutrons, gamma rays and X-rays, which cause ionization when passing through the matter, and is specifically divided into direct ionizing radiation and indirect ionizing radiation. Examples of direct ionizing radiation include alpha rays, beta rays and protons, which have an ability to directly ionize the matter, and examples of indirect ionizing radiation include X-rays, gamma rays, and neutrons, which have no ability to directly ionize the matter but are capable of indirectly ionizing the matter through interaction with the matter.
Non-ionizing radiation whose energy is relatively low to such an extent that charged ions are not produced or an ionization probability is very low when passing through the matter, and examples thereof include infrared rays, visible rays, and UV rays.
Alpha rays are absorbed and blocked by a material having a thickness comparable to that of a sheet of paper, and may be instantly stopped in the air, thus obviating a need to be additionally shielded. The beta rays are known to have energy lower than that of the alpha rays in most cases and may be halted even by a thin aluminum foil or a plastic sheet.
Gamma rays whose energy is greater than that of the X-rays are electromagnetic waves generated from nuclear disintegration or transmutation, and have great penetrating power. Such gamma rays and X-rays may be blocked with concrete or a high-density metallic material such as iron or lead. In the case where the metallic material is used, problems in which the weight of the shielding member is undesirably increased owing to the high density of the metallic material incur.
Neutrons are generated due to nuclear disintegration or fission and are in an uncharged state. In the case of fast neutrons, however, energy is high to the level of 1 MeV or higher, and thus, in order to decelerate the fast neutrons, a material containing a large amount of hydrogen having a mass similar to that of a neutron may be used in combination. Further, there is required a shielding member containing a neutron absorbing material for absorbing thermal neutrons having low energy (˜0.025 eV) resulting from the deceleration of the fast neutrons.
In particular, gamma rays, X-rays or neutrons directly act on atoms or molecules, thus changing the main structure of DNA or proteins. When this type of radiation acts on the generative cell of a living organism, a probability for inducing mutation to thus bring about malformation and malfunction may be increased. In the case where this type of radiation acts on the adult organism, a disease such as cancer may be caused. Moreover, thermal neutrons make the surrounding material radioactive to thus pollute the surrounding environment with radioactivity. Hence, the area to which radiation is applied essentially requires a radiation shielding member able to shield gamma rays, X-rays or neutrons harmful to the human body and the environment.
Conventionally, gamma rays or X-rays shielding member is known to be imparted with shielding effects by using a material containing iron, lead, and concrete. On the other hand, a neutron shielding member is known to be a mixture of a polymer or metal matrix and a compound including a material having a large thermal neutron absorption cross-section, such as boron, lithium and gadolinium having the ability to absorb thermal neutrons. For example, Korean Patent Publication No. 10-2006-0094712 discloses a shielding member using high-density polyethylene as a polymer matrix in which boron known to absorb thermal neutrons and lead known to decay gamma rays are mixed together in order to be easily processed and shield from both neutrons and gamma rays. However, the above patent does not recognize the fact that the particle size of the radiation shielding material has a great influence on radiation shielding performance.
To date, the performance of the radiation shielding member is known to be determined merely by the properties of radiation shielding material (depending on absorption cross-section in the case of neutrons, or depending on the decay constant in the case of gamma or X-rays), the amount of radiation shielding material in the matrix, and the thickness of the shielding member. The particle size of the radiation shielding material is not known to greatly affect the radiation shielding performance. Further, there is no report related to the preparation of a radiation shielding member using homogeneous dispersion of a radiation shielding material in the form of nano-particles in a polymer matrix.